Television system and method of operation



Nov. 9, 1943. E. F. w. ALEXANDERSON TELEVISION SYSTEM AND METHOD OF OPERATION Filed May 27, 1941 2 Sheets-Sheet l .S055 n m SOX V l l l l l l l 111|.

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TELEVISION SYSTEM AND METHOD OF OPERATION Filed May 27, 1941 2 Sheets-Sheet 2 ?atented Nov. 9, 1943 TELEVISION SYSTEM AND METHOD OF OPERATION Ernst F. W. Alexanderson, Schenectady, N. Y., assignor to General Electric Company, a. corporation of New York Application May 27, 1941, Serial No. 395,414

7 Claims. I (Cl. P18-5.2)

My invention relates to a television system and method of operation and is particularly concerned with the transmission and reproduction of scenes in color.

Present day television practice, conforming to uniform television standards proposed for the United States, is directed to the transmission of both the video and audio television signals within a six megacycle channel, approximately 4.5 megacycles of which is devoted to the video signal. It is also generally accepted practice to employ double-interlaced scanning, wherein successive picture fields are-staggered so that the lines of one field are interlaced with the lines of alternate fields.

This practice has been found to be satisfactory for the transmission of monochrome images and it is highly desirable that the same standards should permit the satisfactory transmission of images in color. For high quality reproduction of television images in natural color it is generally accepted that at least three color components must be transmitted. Systems utilizing three colors have heretofore been proposed. In some of these a plurality of carrier frequency channels are employed and a plurality of image signals, one for each color, are simultaneously transmitted over the respective channels. Obviously, these several channels must occupy a much greater portion of the available frequency spectrum allotted to television transmission than in the case of a single channel, which in turn reduces the number of color television systems which can be accommodated by the channels available for such service.

It has also heretofore been proposed to transmit a plurality of colors over a single channel sequentially, the different image components being received in sufficiently rapid succession so that the images reproduced therefrom create the illusion of a complete image in color when superimposed. It will be apparent that in this type of system the capabilities of the system are incompletely utilized, since only one color image is transmittedat a time. Furthermore, it has not been found possible to produce pictures of acceptable quality when transmitting three colors sequentially and utilizing the present standards as to channel Width and scanning frequencies.

It is possible to produce a two color image of good quality within the present television standards in a system employing sequential transmission of the two color components over a single channel. My Patent 1,988,931, granted January 22, 1935, and assigned to the same assignee as the appended claims.

th`e\present invention, teaches how a television receiver employing no moving parts may trace picture images alternately on two cathode ray devices, one producing arrimage of odd lines in one color, the other producing an image of even lines in a second color. These two images are then superimposed by optical means in order to produce a composite image in the two colors. The present invention embodies certain of the principles set forth in my'prior patent and incorporaties additional features to provide for the transmission of more than two color images over a single channel and the creation of a picture image which more closely simulates the transmitted scene in its natural colors.

Briefly, in preferred embodiments of the present invention, image signals corresponding respectively tc two color components of portions of a scene being televised are generated sequen-A tially. A third image signal, corresponding to a third color component of this scene is also synchronously and continuously generated. The rst two signals are modulated upon a carrier wave Awith one type of modulation and the third signal is concurrently modulated upon the same carrier wave with a different type of modulation. Therefore, at any instant two different signals are simultaneously modulated on the same carrier. At the receiving apparatus the carrier wave is demodulated as to both types of modulation and the resultant image signals are utilized to produce a plurality of images, each in a different color. These images are then superimposed by optical means to produce a composite image, simulating the televised scene in its natural colors.

It is therefore a primary object of my invention to provide an improved television system and method of operation whereby two signals, each conveying information regarding a different optical characteristic of ascene may be transmitted simultaneously over a single television channel,

Another important object of my invention is to provide an-improved color television system and method of operation whereby more than two color components of a scene may be transmitted over a single channel and from which a composite color image of high quality may be reproduced, all within the present day standards of television practice proposed for the transmis-g sion and reception of monochrome images.

The features of my invention which I believe to be novel are set forth with particularity in My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to` the following description taken in connectlon with the accompanying drawings, in which Fig. 1 is a schematic diagram of a television transmitting apparatus embodying my invention; Fig. 2 is a detailed diagram of circuits which may form component parts of the apparatus of Fig. 1; Fig. 3 is a schematic diagram of a television receiving apparatus embodying my invention; Fig. 4 is a detailed diagram of circuits which may form component parts of the apparatus of Fig. 3; and Fig. 5 is a schematic view of a modiiied'form of optical system which may optionally be substituted for those portions of the apparatus of Fig. 3 to the right of the vertical dashed line A-A.

At the left-hand side of Fig. 1 is represented a scene to be transmitted, which may be a person In as illustrated, an object, a picture, a. motion picture iilm, etc. The scene Ill is televised by two separate cameras I I and I2 which produce television image signals in a manner well known to those skilled in the art. 'I'hese signals are combined in a manner now to be described and a resultant television signal containing these and other component signals is radiated from the antenna I3 at the right-hand side of Fig. 1. For clarity of illustration, most of Fig. l, as well as of Fig. 3, has been represented as a one-line circuit diagram, and elements whose constructional details may be conventional have been indicated in schematic block form.

For three color transmission, the scene III is analyzed into three color components, red, green and blue, as is well understood in the art. Thus, as is shown in Fig. 1, the camera II alternately views the scene III through the portions Ila and Mb of the rotating color iilter disk Il. I'he portion Ida has been cross-hatched to indicate that it is a red filter and the portion IIb has been cross-hatched to indicate that it is a blue iilter. 'Ihe camera I2 views the' scene Il through a stationary filter I5 which has been cross-hatched to indicate that it is a green filter.

The cameras II and I2 may comprise any suitable types of image signal generators known to the art, such as the iconoscope," orthicon, or image dissector types of camera tubes, for example. In the schematic representation of Fig. 1 the cameras I I and I2 have been shown widely separated to clarify the drawings. It will of course be understood that it will generally be preferable to employ a suitable optical system, not shown, so that all cameras view the scene III from as nearly the same point as possible.

In the cameras II4 and I2, optical images of the scene I0 are scanned in synchronism to generate image signals which are supplied respectively to the lines I6 and I'I. In accordance with present television practice, double-interlaced scanning is preferably employed. The details of apparatus for effecting the scanning action are familiar to the art and hence the deiiecting and synchronizing circuits are indicated only in simplified block form.

Briefly, the pulse generator I8 produces vertical and horizontal synchronizing pulses which are maintained in a predetermined frequency relationship. For example, in a television system employing 441-line double-interlaced scanning, the frequency of the vertical synchronizing pulses may be 60 cycles per second and the frequency of the horizontal synchronizing pulses 13,230 cycles per second, both of these frequencies being syncessive picture fields.

chronized from the common 60 cycle power supply source. The vertical synchronizing pulses are supplied over the line I9 to the vertical deflection generatoZII and the horizontal synchronizing pulses are supplied over the lline 2I to the horizontal deflection generator 22.

The sweep waves generated by the vertical and horizontal deflection generators 20 and 22 are generally of sawtooth form, as is well understood in the art. Their approximatenwave forms are indicated by the curves 20a and 22a. It will be understood that these curves, as well as other curves shown in Figs. 1 and 3, are only suggestive of weil known wave forms which may be employed and are not necessarily drawn in exact proportions or to the same scale. i

The sweep waves are amplified in the amplifiers 23 and 24 and are supplied over the conductors 25 and 26 to the vertical and horizontal sweep elements of both cameras II and I2 thereby causing them to scan in synchronism over the optical images of the scene to be transmitted.

In the apparatus of Fig. 1, the rotating color disk I I is synchronized with the sweep frequencies supplied to the camera II so that the red filter Ila is interposed between the scene I0 and the camera II during scanning of even lines and the blue filter is interposed during the scanning of odd lines, or vice versa. In other words, a red or blue image is projected upon the camera during alternate picture fields and a blue or red image during intervening picture fields. The synchronization of the color disk I 4 may be accomplished in any suitable manner. As illustrated, it is driven at the proper speed by a synchronous motor 21 which in turn is synchronized with the pulse generator I8 since it is energized from the same power supply source over the conductors 28.

The pulse generator I 8 also generates blanking pulses which are utilized in well-known manner to blank out the image signal generated in the cameras II and I2 during the retrace intervals between successive scanning lines and suc- A blanking signal, generally of the form of curve 29a, is supplied over the line 29 to the mixer 30, in which it is combined with the image signal transmitted over the line I'I. Likewise, the corresponding blanking signal 3Ia is supplied over the line 3| and combined in the mixer 32 with image signals transmitted over the line I 6.

A synchronizing wave of well-known form 33a is also supplied toone of the mixers andadded to the image and blanking signals therein.v As illustrated in Fig. 1, this signal is supplied over the line 33 to the mixer 30, although it will be apparent to those skilled in the art that it may optionally be combined with the signals supplied to the mixer 32.

In accordance with my invention the resultant television signals appearing in the outputs of the mixers 30 and 32 are next concurrently modulated upon a common high frequency carrier wave in the form of two different kinds of modulation. It is well known that a carrier Wave can be modulated in three dierent ways, i. e., in amplitude, frequency or phase. It can also be shown that either frequency or phase modulation and amplitude modulation may be simultaneously impressed upon the same carrier without cross modulation, if proper care is taken in circuit design, particularly where the modulation signals are synchronized as in the present case.

In the transmitting apparatus shown in Fig. 1,

the output of the mixer 30, comprising a complete television signalv generally of the wellknown form shown in the curve 40a, is supplied over the line 40 to an amplitude modulator 4|. Likewise, the output of the mixer 32, which comprises a television signal of the same general form, except for the omission of the synchronizing pulses 33a, is supplied over the line 42 to the frequency modulator 43.

A high frequency carrier wave, generated by the high frequency oscillation generator 44, is modulated both in frequency and in amplitude by the modulators 43 and 4|, respectively. The doubly modulated carrier is then suitably amplified in the power amplifier 45 and radiated from the antenna I3.

As previously mentioned, various specific forms of apparatus may be employed for the various units of the transmitting apparatus just described and their structural details form no part of my invention. However, for completeness of illustration there is represented in Fig. 2 a detailed diagram of circuits which may be employed for the portions of Fig. 1 enclosed within the dashed rectangle 46.

The high frequency generator 44 is represented conventio-nally as a well-known form of oscillator embodying a pentode amplifier 50 which has an anode circuit tuned, in conjunction with certain other elements, to the desired mean carrier frequency. The anode circuit 5| is coupled back to the grid circuit 52 in order to cause generation of sustained oscillations.

The frequency modulator 43 comprises a pentode amplifier 55 which has its anode to cathode space path connected across the anode circuit of the amplifier 50. Voltages developed at the anode of the amplifier 55 are supplied to its control grid through the phase shifting network comprising the capacitor 56 and resistor 51. By properly adjusting the circuit constants, in a manner which will be apparent to those skilled in the art without detailed explanation, tube 55 is made to appear as though it were a reactance across the anode circuit 5|. Therefore, the frequency generated by the oscillator 44 is dependent upon the magnitude of this reactance and the constants of the circuit 5|. This frequency may be varied by varying this reactance in response to signals supplied over the conductors 42 from the mixer 32 and'impressed on the grid circuit of the reactance tube 55.

The amplitude modulator 3| comprises a transformer having a primary winding supplied with signals over the conductors 40 from the mixer 30 and a secondary winding connected in the anode supply circuit for the amplier 50. The amplifier 50,is thereby plate-modulated in conventional manner to vary theamplitude of the carrier wave.

Suitable operating potentials are supplied to the amplifiers 50 and -55 from a source represented conventionally by the battery 58 and power supply potentiometer 59.

Referring next to the receiving apparatus of Fig. 3, modulated carrier waves received at antenna are amplified and converted to waves of an intermediate frequency in the radio frequency amplifier and converter 1| and further amplified in the intermediate frequency amplifier 12. The intermediate frequency carrier vwaves are next demodulated 'both as to amplitude, in the limiter and amplitude modulation detector 13, and as to frequency, in the frequency discriminator 14. One form of apparatus which has been found to be satisfactory for carrying out these functions will shortly be described in greater detail.

The demodulated television signals are supplied to three cathode ray picture tubes 15, 18 and 11. The construction of these tubes is well-known to the art. Each tube includes an electron gun for developing and projecting a cathode ray against a sensitive surface, such as a fluorescent coating upon the end wall of the tube, in order to produce a visible trace. Each tube also includes a ray intensity control electrode, or grid, and a pair of coordinate ray deflecting coils. The signals demodulated in the limiter and amplitude modulation detector 13 are supplied to the grid of the tube 11 over the line 18. 'I'he demodulated signals developed at the output of the frequency discrixninator 14 are supplied over the line 19 to two mixers 88 and 8|, the outputs of which are supplied to the grids of the tubes 15 and 16 over the lines 82 and 83, respectively.

Fig. 4 shows one specific arrangement of circuit elements which I have found to be satisfactory for those portions of Fig. 3 within the dashed rectangle H0. The circuit 13 represented in Fig. 4 is essentially a well-known form of amplitude limiting circuit including a pentode which develops a self-bias across the RC network ||2 through grid current rectification. If the circuit constants are adjusted so that pentode is maintained biased at least to cutoff under all signal conditions, amplitude modulation is largely removed from its anode circuit, as will readily be understood by those skilled in the art. At the same time, amplitude modulation voltages are developed across the network ||2 so that the circuit 13 may also be utilized to perform the additional function of an amplitude modulation detector. The demodulated signals appearing across the network ||2 are supplied to the grid of the cathode ray device 11 over the conductors 18, as previously described in connection with Fig. 3.

The output of the limiter 13 is supplied to the frequency discriminator 14. As represented in Fig. 4, this discriminator is a well-known form of back-to-back detector. Further information on the details of construction and operation of this discriminator circuit may be had by reference to Patent 2,121,103--Seeley granted June 2l, 1938. TheI output of the discriminator 14 is supplied to the mixers and BI over the conductors 19, as previously described.

The synchronizing signal components are separated from the image signal components in the synchronizing pulse separator 90 in a wellknown manner. The separator 90 also separates the vertical synchronizing pulses from the horizontal synchronizing pulses and supplies them over the lines '9| and 92 to the vertical deflection generator 93 and the horizontal deflection generator 94, respectively.

It was previously suggested in connection with the description of Fig. l that the synchronizing signals might optionally be combined with the image signals transmitted by frequency modulation rather than by amplitude modulation. In this case it will be 'apparent that the synchronizing pulse separator 90 of Fig. 3 will "be supplied from the point on the line 19 rather than from the line 18.

The outputs of the deiectionv generators 93 and 94 are supplied to the vertical and horizontal deflecting coils of the cathode ray devices 15, 1B and 11 over the conductors 95 and 9B. The

wave forms of the vertical and horizontal deecting waves developed in the defiecting coils of the cathode ray devices are essentially the same as those supplied to the cameras Il and I2 in the transmitting apparatus of Fig. 1, as is indicated by the curves 93a and lla.

It will thus be apparent that the cathode ray devices in the receiving apparatus are caused to scan in synchronism with the cameras in the transmitting apparatus. The ray in the picture tube 11 is also modulated so as to trace an image corresponding to the image signal generated in the camera I 2. At the same time, if both picture tubes 15 and 16 are permitted to operate simultaneously, e'ach will trace an image corresponding to the complete image signal generated in the camera I I.

It will be recalled that, due to the action of the synchronized rotating color screen I4, the image signals generated by the camera II are alternately representative of diilerent color components in complementary portions of the transmitted scene. In the illustrated embodiment, these signals represent red and blue images of alternate picture ilelds.

In order to have each of the cathode ray devices 15 and 16 trace an image representative only of one color component generated in the camera II, it is necessary to render them alternately inoperative during successive picture elds. For this purpose a multi-vibrator 91 is provided which .generates waves oi' the form indicated generally by the curve 91a. 'I'hese waves have a fundamental frequency equal to the vertical scanning frequency and are synchronized from the synchronizing pulse separator 90 in the same manner as the vertical deection generator. These waves are clipped in the clipper 98 to give them a substantially square wave form, indicated by the curve 98a. They are then supplied to an inverter 99 which provides two kwaves at its output, illustrated by the curves '99a and 99h, which are of the same form as wave 98a except that one is of opposite phase. The output of the inverter is supplied to the mixers 80 and 8|. In the mixer these waves, which may be termed ileld blanking signals, are utilized in a manner which will be apparent to those skilled in the art without detailed explanation, to key the cathode ray tubes 15 and 16 alternately on and oi during successive picture elds.

A partial image of even line scans is now traced by the ray in one of the devices 'I5 and 16 and a complementary partial image of odd line scans is traced by the ray in the other of these devices. At the same time a complete image of both even and odd line scans is traced by the ray in the device 11. If these images are now given colors corresponding to the component colors of the i'llters I4 and I5 in the transmitter, each image will represent one color component of the scene being transmitted. This may be done in various ways. For example, red and blue lters may be placed in front of the tubes 15 and 16 and a green iter in front of the tube 11; or instead of employing color filters in front of the respective tubes, cathode ray tubes may be employed having different kinds of fluorescent materials which iluoresce directly in the desired colors.

The images produced 'oy the tubes 15, 16 and 11 are optically superimposed. In the apparatus of Fig. 3, the tubes 15 and 16 are illustrated as being placed at right angles to each other and equidistant from a semltransparent mirror IIII at 45 to their axes. Similarly, the Atubes 16 and 11 are placed at right angles to each other and equidistant from a second semi-transparent mir-4 ror IUI, which is also at 45 to their axes. The eye of an observer, represented at |62, will now observe the three images in superimposed relation. If the colors of the several images are properly proportionedrand if the densities of thesemitransparent mirrors I" and ,IIII are properly adiusted', the transmitted scene will be closely simulated in its natural colors.

It will of course be understood that the intensities ofthe several component images may be adjusted in various dinerent ways known to the art so that the composite image reproduces the correct color values o! the transmitted scene. Merely by way of example, the relative intensities of the image signals may be controlled in the transmitter of Fig. 1 by adjusting the densities of the color screens Ila, IIb and I5, Ior the sensitivities of the image signal generators II and I2, or the signal gains through the mixers 3| and 32. Similar adjustments may also be made in the receiving apparatus of Fig. 2. For example, instead of proportioning the densitiesv of the semi-transparent mirrors I" and IIII to give the proper absorption and reilection characteristics, as. suggested in the preceding paragraph, the relative image intensities may be controlled by adjusting the signal gains through the ampliers and mixersfll, 12, 8l and II, or the control grid bias voltages applied to tubes 15, 16 and 11, or the response characteristics oi' the fluorescent screens of tubes 15, 16 and 11.

Fig. 5 diagrammatically represents a modification of the optical system of Fig. 3, to the right of the vertical dashed line A-A. Corresponding p reference numerals have been applied to corresponding elements in the two gures. In thisaccordance with my invention and will still re-` produce a good picture in black and white. This results from the fact that the ordinary amplitude modulation receiver will respond to both amplitude modulation and frequency modulation but will not discriminate between the two. Since the two modulation signals are transmitted in syn` chronism they will produce no interference with each other in this case. i

It is also a relatively simple matter to convert an ordinary monochrome receiver to a color television receiver capable of receiving two of the three color components, providing the receiver is located inthe same power service area as .the transmitter. To accomplish this result. it is only v necessary to utilize a rotating color screen similar to the color screen I4 in the transmitter driven by a synchronous motor similar to the motor 21v and supplied with power from the same common power supply source. two color picture produced in this manner is of reasonably good quality and such a receiver may It has been shown that a well supply a commercial need in the lower price ranges.

It will of course be understood that many other modifications may be made in the specific apparatus employed to carry out my invention in its broadest aspects. The image signal conveying information as tothe two color components may of course be modulated upon the carrier wave as amplitude modulation, and the image signal continuously conveying the third color component be transmitted as frequency modulation. Furthermore, as previously mentioned, phase modulation, employing known methods andapparatus, may be utilized instead of frequency modulation if deslr'ed.

It may be desirable under some conditions tol use other modes of transmitting the two types of modulation over a single carrier channel. For example, one television signal, preferably the signal conveying two color components, may be modulated directly upon a main carrier wave, either as amplitude modulation or frequency modulation, and the other television signal modulated upon a sub-carrier wave having a relatively low frequency lying within the standard television channel, e. g., 4 megacycles. The modulated sub-carrier is then in turn modulated upon the main carrier. It will be understood that the frequency bands occupied by the television signals will necessarily be restricted in this case to prevent interference between them. Thus, the rst signal may have a band width of about 3.0 mc. It has been shown that a picture reproduced from an image transmitted over a channel of this width is satisfactory for practical purposes. A sub-carrier channel of about 1.5 mc. width is then available to the second signal within the standard 4.5 mc. channel. The picture image reproduced from the signal transmitted over this narrower channel will of course not have quite as sharp definition as the picture transmitted in the three megacycle channel, but this will not be necessary because the deilnition in the complete colored picture will be determined by the first signal, whereas the second signal will be used to secure the correct color values.

The transmitting apparatus of Fig. 1 may readily be modified so as to eliminate all moving parts in the transmitter. This may be C one by replacing the camera I l of Fig. 1 by two cameras, cach of which has a stationary color lter in front of it corresponding to one of the sections I 4a and I4b of the rotating color filter illustrated. The outputs of these two cameras will be combined to form a complete image signal exactly like the signals supplied from the camera` ll to the mixer 32 in Fig. 1. complishing this may be the exact counterpart The apparatus for acof that shown and described in connection with receiver of Fig. 3. Thus, it will be necessary to pass the image signals generated in each camera into mixers similar to the mixers 80 and 8| of Fig. 3 and to inject eld blanking pulses into these mixers in order to blank out alternate fields in the two cameras. The apparatus for accomplishing this may be the-same as the multivibrator 91, clipper 98 and inverter 99 of Fig. 3, all being synchronized from the pulse generator I8 of Fig. 1. The remainder of the transmitting apparatus of Fig. l will require no\further modication.

It will be .apparent that I have provided an efficient and flexible method and apparatus for transmission and reception of multi-color television pictures of high quality over' a single television channel, and furthermore, one which doeg not require the adoption of new standards dif-- fering essentially from those recommended for present monochrome television practice. Wnile 1 have shown and described particular forms of apparatus which I believe to be best suited for the vpractice of my invention, it will of course be understood that other modifications may be made, and I contemplate by the appended claims to cover any modifications that fau within the' true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In the art of color television, the method of operation which comprises the steps of scanning a colored scene to produce an image signal conveying information alternately representative of two different color characteristics of said scene, independently and synchronously scanning said scene to produce a second image signal representative of a third color characteristic of said scene, concurrently modulating a carrier wave in frequency or phase by one of said signals and in amplitude by the other of said signals, transmitting said doubly modulated carrier wave over a single transmission channel, demodulating said carrier wave as to both frequency or phase and amplitude to produce picture signals corresponding respectively to said image signals, producing a plurality of picture images from said picture signals each corresponding to one of said color characteristics, and optically superimposing said images to create a composite picture image simulating said scene in its natural colors.

2. A color television system comprising, in combination, means for generating a plurality of television image signals each representative of one or more selected color components of a scene,

of modulation alternately in accordance with at least two of said signals, means for concurrently modulating said carrier with a. second type of modulation in accordance with anotherof said signals, means for demodulating said carrier as to both of said types of modulation to produce video signals corresponding respectively to said image signals, means for producing a plurality of colored picture images from said video signals, each corresponding to one of the respective color components of said scene, and means for optically superimposing said images for simultaneous observation.

3. In the art of color television, the method`of operation which comprises the steps of scanning a predetermined area of a colored scene and generating a first image signal conveying information of a first color component of said scene over said entire area, synchronously scanning said object and generating a second image signal conveying information of a second color component of said scene over at least a selected portion of said area and also generating a third image signal conveying information of a third color component of said scene over at least the remaining portion of said area, combining said second and third signals to form a fourth image signal conveying information of said secondand third color coinponents over said selected and remaining portions respectively, modulating a high frequency carrier wave with a first type of modulation representative of said first signal and with a second type of` 4. In a color television system, the combination comprising means for effecting double-interlaced scanning of a colored scene to produce a complete televlsion image signal corresponding to one color characteristic of said scene, means iorsynchronously eiecting even-line scanning andl oddline scanning of said scene to produce two partial image signals corresponding respecti ely to second and third color characteristics of d scene, means for combining said second and hird signals to form a second complete television image signal, means for modulating a carrier wave in frequency or phase by one of said complete signals, means for modulating the same carrier wave in amplitude by the other of said complete signals, and means ior transmitting said doubly modulated carrier wave over a single channel.

5. In a television system, the combination comprising a nrst channel adapted to translate a carrier wave which may be modulated both in frequency orphase and in amplitude bytelevision signals, means in said channel for separating both types of television signals from said wave and supplying them to second and third channels, three cathode ray devices each having means therein for developing, modulating and deilecting a cathode ray, means for energizing all said deectlng means in synchronism, means for supplying signals from said second channel to the modulating means of one device and from the third channel to the modulating means ot both the other two devices, and means for rendering said other two devices respectively operative and inoperative inA alternation at a predetermined rate.

6. In a color television system, the combination comprising, a ilrst channel adapted to translate a carrier wave modulated in frequency or phase and in amplitude by two synchronized television signals, one of said signals conveying information f as to aifirst color component of a scene'and the other of said signals alternately conveying infomation as to second and'third color components of complementary portions of said scene, means in said channel -for separating said television signals from said wave and supplying themV respectively to second and third channels, three assenso cathode ray devices eachhaving means therein for developing and projecting a ray against an image screen. ray modulation means and coordinate ray deilecting means, means for energizing said ray deecting means to cause said three devices to scan in synchronism with each other and with said signals, meansfor supplying signals from said second channel to the modulating means of one device and from the third channel to the modulating means oi' both the other two devices, means for rendering said other two devices alternately operative and inoperative in synchronism with the alternatlons in said other television signaLmeans to give the image traced by each device a diii'erent color, and means for superimposing said images.

7. In a color television system having means for receiving a carrier wave lying within a single channel and modulated in frequency or phase by an image signal and in amplitude by another Aimage signal, said signals resulting from synchronized double-interlaced scanning of a colored scene, a first one of said signals corresponding to one color component in said scene and the second oi' said signals having`odd line scans corresponding to a second color component and even line scans corresponding to a third color component, means for demoduiating said wave both as to frequency orphase, and as to amplitude to reproduce said image signals, three cathode ray devices each having means therein for projecting a ray against an image screen, means for causing all of said rays to scan said screens in synchronism with said signals, means for modulating the intensity of oneray in accordance with said i'irst signal, means for modulating the intensities of both the other rays in accordance with said second signal, means for blanking out even line scans of one of said two rays and odd line scans ot the other oi' said two rays, means to give the image traced by each ray a color corresponding to the color component conveyed by the modulating signal during active scans, and means for optically superimposing said images to form a composite image simulating said scene in its natural colors.

ERNST F. W. ALEXANDERsoN. 

